Electronic Material Science and Engineering

A main topic of our laboratory (Matsushige Lab) is basic and application research of organic molecular materials, which are highly expected to show new electronic and optical functions at a nanometer scale. Several active research projects are running in our lab, which widely include new instrumentation based on "Advanced Nanoprobe Technology", developments of "Nanoscale Manipulation Techniques of Single Molecules" and "Organic Electronic Thin-Film Devices", investigation and application of electronic and optical properties of organic materials and photocatalysts. We are aiming at innovation of new-generation electronic devices through these exciting studies.

Selected Topics of Our Research

Establishment of real-space structural and functional analysis at an atomic/molecular scale is absolutely necessary for evaluating various electronic properties in a system of single or a small number of organic molecules. A main purpose of this study is developing dynamic-mode atomic force microscopy (DFM) with a real atomic resolution for all surfaces under various surroundings (e.g., in air, in vacuum, in water, etc.), and we are proceeding toward the development of multi-functional analytical probe microscopes capable of local measurements of optical and electronic properties.

The final goal of this study is employment of these methods for nanoscale characterization of functional organic layers, inorganic semiconductors, carbon nanotubes, biomaterials, for the purpose of making guidelines for development of new-generation nanoscale devices.

Control of Structure and Orientation of Functional Organic Molecules and its Device Application

Organic Molecules own some excellent characteristics as electronic material, such as flexibility, low-weight and simple fabrication processes. This feature indicates some potential for creating new industrial fields of innovative flexible (nanoscale) electronic devices. However, control of crystalline structures and molecular orientation inside ultrathin layers or thicker films is of great importance for functionalizing each molecule sufficiently, because of strong anisotropy of optical and electronic properties of molecules. In this background, our group continues fabrication of thin films with various functional organic molecules, and those characterizations with original X-ray diffraction and other spectroscopic methods, electrical measurements and so on. We aim at the development of highly-efficient control methods of organic thin-film structures for generating supreme performance of electronic properties.

For example, device characteristics (e.g., carrier mobility and threshold voltage) of organic field-effect transistors (OFETs) made of organic semiconductors such as pentacene, oligothiophene are mainly determined by crystalline phase and molecular orientation of organic semiconducting layers. Interfaces between gate insulators and organic semiconducting layers give large influences to OFET performance. In our group, control of OFET characteristics and elucidation of its operation have been attempted with structural control of organic semiconducting layers and insertion of gate buffer layers.

Besides, organic ferroelectric materials have been intensely studied in our group for a long time. Ferroelectricity of organic materials derives from molecular rotation, propagation of conformation and other intermolecular cooperative motions, which are characteristics of only organic (polymer) materials. Now our research is directed toward both investigation of these ferroelectric properties and application of organic ferroelectrics to ultrahigh-density nonvolatile memories and other ferroelectric devices.

Optical and electronic phenomena of titanium dioxide thin films have been examined according to the following topics.

"Development of new evaluation method of electron mobility using field-effect transistor structures with liquid gate electrode"

The objective of this study is evaluating electron mobility of TiO2 thin-films immersed in electrolytes, which are widely used as electron transport layers of dye-sensitized solar cells (DSSCs). We hope that this new method would contribute to the improvement of energy conversion efficiency of DSSCs.

"Photocatalytic hydrogen production in high vacuum"

Photocatalytic hydrogen production from gaseous methanol and water was first detected in a high vacuum condition for platinum-loaded TiO2 films, using our newly-developed vacuum system with quadrupole mass spectrometer. This new method is suitable for evaluating sensitively photocatalytic activities in high vacuum at a real-time scale. We expect that this new mechanism of solar hydrogen production using gas-phase molecules might be possibly applied to high-speed hydrogen production in the future.

"Direct observation of photocatalytic surfaces and those electronic properties under ultraviolet-ray(UV) irradiation"

In order to know details of photocatalytic surface states under UV irradiation and complicated mechanisms of photocatalytic reactions, direct observation of photocatalytic surfaces and those electronic properties under UV irradiation are tried with surface X-ray diffraction, Kelvin Probe Force Microscopy and other special techniques.